1. Field of the Invention
The present invention relates to voltage isolation barriers, and in particular, to solid-state voltage isolation buffers which allow information to be transmitted across the voltage isolation barrier via a magnetic field.
2. Description of Related Art
Many electronic systems, such as industrial control systems, require some form of electrical isolation in order to protect circuits from large voltage spikes. A benefit to electrical isolation is the avoidance of ground loops that significantly increase system noise. Other benefits are related to protecting people from electrical shock hazards.
Electrical isolation buffers relate to the transfer of information between electrical systems. When dissimilar electrical systems are linked by electrical isolation buffers, the electrical isolation buffers serve to translate information from one electrical system to the other electrical system.
Various electrical isolation technologies have been used in the past to translate information from one electrical system to another electrical system. For example, some electrical isolation technologies transmit AC coupled signals through capacitors or transformers. Optical coupled technologies convert electrical signals to optical signals transmit the optical signal to an optical receiver, which then converts the optical signal back to an electrical signal.
Other electrical isolation technologies use magnetic field sensors to measure the magnetic field generated by a signal current flowing in a coil of wire. For example, U.S. Pat. Nos. 4,020,294, 4,441,072, and 4,616,188 describe various Hall effect voltage isolation circuits that measure the magnetic field generated by signal current flowing in a coil of wire. However, these patents fail to address the problem that, in general, the performance of silicon based Hall effect sensors suffers due to large variations in magnetic field sensitivities and variations in DC-offset due to temperature changes. Additional information regarding the Hall effect in silicon circuits may be found in the article by J. T. Maupin and M. L. Geske entitled “The Hall Effect in Silicon Circuits.” Symposium on Hall Effect and Its Applications, Johns Hopkins University, 1979, Plenum Press, New York, the contents of which are specifically incorporated herein by reference.
Various attempts have been made to correct for temperature changes in Hall effect sensors. For example, U.S. Pat. Nos. 4,833,406 and 5,055,768 describe various techniques to achieve fairly constant magnetic field sensitivity over a range of temperatures. U.S. Pat. No. 5,621,319 describes a technique to reduce the DC-offset of a Hall effect sensor. However, to achieve an optimal performing voltage isolation buffer utilizing a Hall effect sensor as the magnetic field sensor, it is desirable that both DC-offset variations and magnetic field sensitivity variations be greatly reduced.
The patents and references cited herein are specifically incorporated by reference to the maximum extent allowable by law.